Introduction: Biliary tract infection is an important source of bacteraemia. Frequently, polymicrobial blood stream infections (BSI) are also of biliary origin. The aim of our study was to compare monomicrobial (M) with polymicrobial (P) BSIs of biliary origin in terms of epidemiology, aetiology, severity and outcome.

Material and Methods: From Jan 2000 to June 2006, all adult cases of BSI from a biliary source were identified through records of the Clinical Microbiology Laboratory in a 450-bed acute care teaching hospital. Medical charts were retrospectively reviewed. Variables included demographics, aetiology, comorbidities, severity of disease, and mortality.

Results: During the study period, a total of 2,260 BSI were recorded; of these, 106 (4.7%) were polymicrobial, and one third (31 episodes) of them were of biliary origin. These 31 episodes represent a 14.8% of all BSI of biliary origin seen during this period. Men (66% vs 45%; p = 0.028), older age (76 y vs 70 y; p = 0.019), and the presence of stones (41% vs 19.2%; p = 0.046) were more frequent in the M group. Comorbidities (Charlson score mean 3.3 vs 2.3; p = 0.039), CPR levels (198 vs 115; p = 0.008), the presence of biliary neoplasia (14.8% vs 4.2%; p = 0.005) or biliary prostheses (25% vs 6.3%; p = 0.006) were more frequent in the polymicrobial bacteraemia group. E. coli was the most frequently isolated microorganism in both groups. Previous surgery or endoscopic retrograde cholangiopancreatography were identified in 18.8% in the M group vs. 26.9% in P (NS), and in 35% in M vs. 22.2% in P (NS), respectively. Severity, defined by the presence of shock, ICU admission or vasoactive drugs requirement, was similar in both groups. Mortality was higher in the polymicrobial bacteraemia group [10% in M vs 19% in P; p = 0.217)].

Conclusions: Biliary tract infection is an important cause of polymicrobial bacteraemia, a third of all cases of polymicrobial bacteraemias seen during a six year period were of biliary origin. It is associated with higher co morbidity as compared with the cases of monomicrobial bacteraemia from the same source. Finally, biliary neoplasm and biliary prosthesis appear to be risk factors for polymicrobial bacteraemia among patients with BSI of biliary origin